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authorFengguang Wu <wfg@mail.ustc.edu.cn>2007-07-19 01:48:04 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-07-19 10:04:44 -0700
commitc743d96b6d2ff55a94df7b5ac7c74987bb9c343b (patch)
tree391e5dad21e62590e343c63e5ba05322d0fc76ad /mm/readahead.c
parentdc7868fcb9a73990e6f30371c1be465c436a7a7f (diff)
downloadlinux-c743d96b6d2ff55a94df7b5ac7c74987bb9c343b.tar.gz
readahead: remove the old algorithm
Remove the old readahead algorithm. Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn> Cc: Steven Pratt <slpratt@austin.ibm.com> Cc: Ram Pai <linuxram@us.ibm.com> Cc: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/readahead.c')
-rw-r--r--mm/readahead.c373
1 files changed, 25 insertions, 348 deletions
diff --git a/mm/readahead.c b/mm/readahead.c
index c094e4f5a25..5b3c9b7d70f 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -49,82 +49,6 @@ file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)
}
EXPORT_SYMBOL_GPL(file_ra_state_init);
-/*
- * Return max readahead size for this inode in number-of-pages.
- */
-static inline unsigned long get_max_readahead(struct file_ra_state *ra)
-{
- return ra->ra_pages;
-}
-
-static inline unsigned long get_min_readahead(struct file_ra_state *ra)
-{
- return MIN_RA_PAGES;
-}
-
-static inline void reset_ahead_window(struct file_ra_state *ra)
-{
- /*
- * ... but preserve ahead_start + ahead_size value,
- * see 'recheck:' label in page_cache_readahead().
- * Note: We never use ->ahead_size as rvalue without
- * checking ->ahead_start != 0 first.
- */
- ra->ahead_size += ra->ahead_start;
- ra->ahead_start = 0;
-}
-
-static inline void ra_off(struct file_ra_state *ra)
-{
- ra->start = 0;
- ra->flags = 0;
- ra->size = 0;
- reset_ahead_window(ra);
- return;
-}
-
-/*
- * Set the initial window size, round to next power of 2 and square
- * for small size, x 4 for medium, and x 2 for large
- * for 128k (32 page) max ra
- * 1-8 page = 32k initial, > 8 page = 128k initial
- */
-static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
-{
- unsigned long newsize = roundup_pow_of_two(size);
-
- if (newsize <= max / 32)
- newsize = newsize * 4;
- else if (newsize <= max / 4)
- newsize = newsize * 2;
- else
- newsize = max;
- return newsize;
-}
-
-/*
- * Set the new window size, this is called only when I/O is to be submitted,
- * not for each call to readahead. If a cache miss occured, reduce next I/O
- * size, else increase depending on how close to max we are.
- */
-static inline unsigned long get_next_ra_size(struct file_ra_state *ra)
-{
- unsigned long max = get_max_readahead(ra);
- unsigned long min = get_min_readahead(ra);
- unsigned long cur = ra->size;
- unsigned long newsize;
-
- if (ra->flags & RA_FLAG_MISS) {
- ra->flags &= ~RA_FLAG_MISS;
- newsize = max((cur - 2), min);
- } else if (cur < max / 16) {
- newsize = 4 * cur;
- } else {
- newsize = 2 * cur;
- }
- return min(newsize, max);
-}
-
#define list_to_page(head) (list_entry((head)->prev, struct page, lru))
/**
@@ -201,66 +125,6 @@ out:
}
/*
- * Readahead design.
- *
- * The fields in struct file_ra_state represent the most-recently-executed
- * readahead attempt:
- *
- * start: Page index at which we started the readahead
- * size: Number of pages in that read
- * Together, these form the "current window".
- * Together, start and size represent the `readahead window'.
- * prev_index: The page which the readahead algorithm most-recently inspected.
- * It is mainly used to detect sequential file reading.
- * If page_cache_readahead sees that it is again being called for
- * a page which it just looked at, it can return immediately without
- * making any state changes.
- * offset: Offset in the prev_index where the last read ended - used for
- * detection of sequential file reading.
- * ahead_start,
- * ahead_size: Together, these form the "ahead window".
- * ra_pages: The externally controlled max readahead for this fd.
- *
- * When readahead is in the off state (size == 0), readahead is disabled.
- * In this state, prev_index is used to detect the resumption of sequential I/O.
- *
- * The readahead code manages two windows - the "current" and the "ahead"
- * windows. The intent is that while the application is walking the pages
- * in the current window, I/O is underway on the ahead window. When the
- * current window is fully traversed, it is replaced by the ahead window
- * and the ahead window is invalidated. When this copying happens, the
- * new current window's pages are probably still locked. So
- * we submit a new batch of I/O immediately, creating a new ahead window.
- *
- * So:
- *
- * ----|----------------|----------------|-----
- * ^start ^start+size
- * ^ahead_start ^ahead_start+ahead_size
- *
- * ^ When this page is read, we submit I/O for the
- * ahead window.
- *
- * A `readahead hit' occurs when a read request is made against a page which is
- * the next sequential page. Ahead window calculations are done only when it
- * is time to submit a new IO. The code ramps up the size agressively at first,
- * but slow down as it approaches max_readhead.
- *
- * Any seek/ramdom IO will result in readahead being turned off. It will resume
- * at the first sequential access.
- *
- * There is a special-case: if the first page which the application tries to
- * read happens to be the first page of the file, it is assumed that a linear
- * read is about to happen and the window is immediately set to the initial size
- * based on I/O request size and the max_readahead.
- *
- * This function is to be called for every read request, rather than when
- * it is time to perform readahead. It is called only once for the entire I/O
- * regardless of size unless readahead is unable to start enough I/O to satisfy
- * the request (I/O request > max_readahead).
- */
-
-/*
* do_page_cache_readahead actually reads a chunk of disk. It allocates all
* the pages first, then submits them all for I/O. This avoids the very bad
* behaviour which would occur if page allocations are causing VM writeback.
@@ -295,7 +159,7 @@ __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
read_lock_irq(&mapping->tree_lock);
for (page_idx = 0; page_idx < nr_to_read; page_idx++) {
pgoff_t page_offset = offset + page_idx;
-
+
if (page_offset > end_index)
break;
@@ -361,28 +225,6 @@ int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
}
/*
- * Check how effective readahead is being. If the amount of started IO is
- * less than expected then the file is partly or fully in pagecache and
- * readahead isn't helping.
- *
- */
-static inline int check_ra_success(struct file_ra_state *ra,
- unsigned long nr_to_read, unsigned long actual)
-{
- if (actual == 0) {
- ra->cache_hit += nr_to_read;
- if (ra->cache_hit >= VM_MAX_CACHE_HIT) {
- ra_off(ra);
- ra->flags |= RA_FLAG_INCACHE;
- return 0;
- }
- } else {
- ra->cache_hit=0;
- }
- return 1;
-}
-
-/*
* This version skips the IO if the queue is read-congested, and will tell the
* block layer to abandon the readahead if request allocation would block.
*
@@ -399,191 +241,6 @@ int do_page_cache_readahead(struct address_space *mapping, struct file *filp,
}
/*
- * Read 'nr_to_read' pages starting at page 'offset'. If the flag 'block'
- * is set wait till the read completes. Otherwise attempt to read without
- * blocking.
- * Returns 1 meaning 'success' if read is successful without switching off
- * readahead mode. Otherwise return failure.
- */
-static int
-blockable_page_cache_readahead(struct address_space *mapping, struct file *filp,
- pgoff_t offset, unsigned long nr_to_read,
- struct file_ra_state *ra, int block)
-{
- int actual;
-
- if (!block && bdi_read_congested(mapping->backing_dev_info))
- return 0;
-
- actual = __do_page_cache_readahead(mapping, filp, offset, nr_to_read, 0);
-
- return check_ra_success(ra, nr_to_read, actual);
-}
-
-static int make_ahead_window(struct address_space *mapping, struct file *filp,
- struct file_ra_state *ra, int force)
-{
- int block, ret;
-
- ra->ahead_size = get_next_ra_size(ra);
- ra->ahead_start = ra->start + ra->size;
-
- block = force || (ra->prev_index >= ra->ahead_start);
- ret = blockable_page_cache_readahead(mapping, filp,
- ra->ahead_start, ra->ahead_size, ra, block);
-
- if (!ret && !force) {
- /* A read failure in blocking mode, implies pages are
- * all cached. So we can safely assume we have taken
- * care of all the pages requested in this call.
- * A read failure in non-blocking mode, implies we are
- * reading more pages than requested in this call. So
- * we safely assume we have taken care of all the pages
- * requested in this call.
- *
- * Just reset the ahead window in case we failed due to
- * congestion. The ahead window will any way be closed
- * in case we failed due to excessive page cache hits.
- */
- reset_ahead_window(ra);
- }
-
- return ret;
-}
-
-/**
- * page_cache_readahead - generic adaptive readahead
- * @mapping: address_space which holds the pagecache and I/O vectors
- * @ra: file_ra_state which holds the readahead state
- * @filp: passed on to ->readpage() and ->readpages()
- * @offset: start offset into @mapping, in PAGE_CACHE_SIZE units
- * @req_size: hint: total size of the read which the caller is performing in
- * PAGE_CACHE_SIZE units
- *
- * page_cache_readahead() is the main function. It performs the adaptive
- * readahead window size management and submits the readahead I/O.
- *
- * Note that @filp is purely used for passing on to the ->readpage[s]()
- * handler: it may refer to a different file from @mapping (so we may not use
- * @filp->f_mapping or @filp->f_path.dentry->d_inode here).
- * Also, @ra may not be equal to &@filp->f_ra.
- *
- */
-unsigned long
-page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra,
- struct file *filp, pgoff_t offset, unsigned long req_size)
-{
- unsigned long max, newsize;
- int sequential;
-
- /*
- * We avoid doing extra work and bogusly perturbing the readahead
- * window expansion logic.
- */
- if (offset == ra->prev_index && --req_size)
- ++offset;
-
- /* Note that prev_index == -1 if it is a first read */
- sequential = (offset == ra->prev_index + 1);
- ra->prev_index = offset;
- ra->prev_offset = 0;
-
- max = get_max_readahead(ra);
- newsize = min(req_size, max);
-
- /* No readahead or sub-page sized read or file already in cache */
- if (newsize == 0 || (ra->flags & RA_FLAG_INCACHE))
- goto out;
-
- ra->prev_index += newsize - 1;
-
- /*
- * Special case - first read at start of file. We'll assume it's
- * a whole-file read and grow the window fast. Or detect first
- * sequential access
- */
- if (sequential && ra->size == 0) {
- ra->size = get_init_ra_size(newsize, max);
- ra->start = offset;
- if (!blockable_page_cache_readahead(mapping, filp, offset,
- ra->size, ra, 1))
- goto out;
-
- /*
- * If the request size is larger than our max readahead, we
- * at least want to be sure that we get 2 IOs in flight and
- * we know that we will definitly need the new I/O.
- * once we do this, subsequent calls should be able to overlap
- * IOs,* thus preventing stalls. so issue the ahead window
- * immediately.
- */
- if (req_size >= max)
- make_ahead_window(mapping, filp, ra, 1);
-
- goto out;
- }
-
- /*
- * Now handle the random case:
- * partial page reads and first access were handled above,
- * so this must be the next page otherwise it is random
- */
- if (!sequential) {
- ra_off(ra);
- blockable_page_cache_readahead(mapping, filp, offset,
- newsize, ra, 1);
- goto out;
- }
-
- /*
- * If we get here we are doing sequential IO and this was not the first
- * occurence (ie we have an existing window)
- */
- if (ra->ahead_start == 0) { /* no ahead window yet */
- if (!make_ahead_window(mapping, filp, ra, 0))
- goto recheck;
- }
-
- /*
- * Already have an ahead window, check if we crossed into it.
- * If so, shift windows and issue a new ahead window.
- * Only return the #pages that are in the current window, so that
- * we get called back on the first page of the ahead window which
- * will allow us to submit more IO.
- */
- if (ra->prev_index >= ra->ahead_start) {
- ra->start = ra->ahead_start;
- ra->size = ra->ahead_size;
- make_ahead_window(mapping, filp, ra, 0);
-recheck:
- /* prev_index shouldn't overrun the ahead window */
- ra->prev_index = min(ra->prev_index,
- ra->ahead_start + ra->ahead_size - 1);
- }
-
-out:
- return ra->prev_index + 1;
-}
-EXPORT_SYMBOL_GPL(page_cache_readahead);
-
-/*
- * handle_ra_miss() is called when it is known that a page which should have
- * been present in the pagecache (we just did some readahead there) was in fact
- * not found. This will happen if it was evicted by the VM (readahead
- * thrashing)
- *
- * Turn on the cache miss flag in the RA struct, this will cause the RA code
- * to reduce the RA size on the next read.
- */
-void handle_ra_miss(struct address_space *mapping,
- struct file_ra_state *ra, pgoff_t offset)
-{
- ra->flags |= RA_FLAG_MISS;
- ra->flags &= ~RA_FLAG_INCACHE;
- ra->cache_hit = 0;
-}
-
-/*
* Given a desired number of PAGE_CACHE_SIZE readahead pages, return a
* sensible upper limit.
*/
@@ -613,19 +270,39 @@ unsigned long ra_submit(struct file_ra_state *ra,
EXPORT_SYMBOL_GPL(ra_submit);
/*
+ * Set the initial window size, round to next power of 2 and square
+ * for small size, x 4 for medium, and x 2 for large
+ * for 128k (32 page) max ra
+ * 1-8 page = 32k initial, > 8 page = 128k initial
+ */
+static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
+{
+ unsigned long newsize = roundup_pow_of_two(size);
+
+ if (newsize <= max / 32)
+ newsize = newsize * 4;
+ else if (newsize <= max / 4)
+ newsize = newsize * 2;
+ else
+ newsize = max;
+
+ return newsize;
+}
+
+/*
* Get the previous window size, ramp it up, and
* return it as the new window size.
*/
-static unsigned long get_next_ra_size2(struct file_ra_state *ra,
+static unsigned long get_next_ra_size(struct file_ra_state *ra,
unsigned long max)
{
unsigned long cur = ra->readahead_index - ra->ra_index;
unsigned long newsize;
if (cur < max / 16)
- newsize = cur * 4;
+ newsize = 4 * cur;
else
- newsize = cur * 2;
+ newsize = 2 * cur;
return min(newsize, max);
}
@@ -701,7 +378,7 @@ ondemand_readahead(struct address_space *mapping,
if (offset && (offset == ra->lookahead_index ||
offset == ra->readahead_index)) {
ra_index = ra->readahead_index;
- ra_size = get_next_ra_size2(ra, max);
+ ra_size = get_next_ra_size(ra, max);
la_size = ra_size;
goto fill_ra;
}